DuPont Co. had improved earnings of $1.59 a share in the second quarter over $1.31 a year ago in spite of a special charge of 24 cents a share.

The special charge was for a reserve resulting from the recently announced decision to discontinue dye-stuff operations.

Net income was $232.8 million on sales of $3.24 billion, up from $190.8 million on sales of $2.73 billion.

First-half profit was $481.2 million ($3.29 a share) on sales of $6.26 billion compared with $353.9 million ($2.16) a year earlier when first-half sales were $528 billion.

The 1978 results are restated to reflect a three-for-one stock split.

Aluminum Co. of America reported second-quarter net income of $134.4 million ($3.81 a share) compared with $74.8 million ($2.13) for the same period last year.

The increase was linked to heavy demand in the aerospace and packaging markets. Alcoa also reported a nonrecurring gain of $12.3 million (35 cents) from the sale of its share in Interway Corp.

Chairman W. H. Krome George said he expects strong demand for the rest of the year.

Revenues during the quarter totaled $1.18 billion compared with $1.01 billion for the same period of 1978.

Shipments for the second quarter were 469,000 tons, and production reached 393,000 tons compared with shipments of 444,000 tons and primary production of 380,000 tons a year earlier.

First-half net income was $262.1 million ($7.43) compared with $128.7 million ($3.66) in 1978. Revenues were $2.38 billion compared with $1.95 billion.

The grounding of the DC10s and a strike at rival United Airlines produced a sharp increase in profits for Trans World Airlines, TWA's parent company reported yesterday.

Trans World Corp. which also owns Canteen Corp. and Hilton International, reported second-quarter earnings of $58.8 million ($3.42 a share), up 18.9 percent from $49.5 million ($2.85) in the same quarter of 1978.

TWA doesn't own any DC10s

Hilton International, which operates Hilton Hotels around the world, but not in the United States, reported pretax profits of $15.5 million, up 15.1 percent. Canteen Corp. pretax earnings rose 43.2 percent to $6.6 million.

For the first six months, Trans World Corp. earnings were $11.0 million, down $900,000 from the previous year. Earnings per share slipped from 35 cents to 28 cents for the half.

Union carbide corp. had a 41 percent sales increase over a year ago in the second quarter and earnings increased to $2.30 a share from $1.65.

But Chairman William S. Sneath said the return of only 6.6 percent on sales was well below expectations.

Net income was $150.5 million on sales of $2.29 billion compared with $106.8 million on sales of $1.98 billion.

First-half net was $275.1 million ($4.21 a share) on sales of $4.45 billion compared with $185.7 million ($2.87) a year ago on sales of $3.8 billion.

Sneath said physical sales rather than price rises accounted for most of the 21 percent gain in domestic sales. He said all the company's operations contributed to the gains.

General Telephone & Electronics Corp. reported a 14 percent gain in telephone revenues in the second quarter and a rise in profits to $1.10 a income was $167.64 million against $143.46 million.

First-half profit was $315.97 million ($2.07 a share), up from $298.24 million ($2.02).

Telephone revenues in the half were up 13 percent at $2.543 billion and product sales were 14 percent higher than a year ago at $21.151 billion.

Monsanto Corp.'s decision to close its European nylon operations caused a dip in second-quarter earnings to $1.64 a share from $2.09 a share a year earlier on an increase of sales to $1.53 billion from $1.19 billion.

Net income totaled $59.5 million after a writeoff for the closed operations of $42.7 million ($1.18 a share). The company also had foreign currency translation losses of 29 cents a share in the quarter. A year earlier, net income was $76.1 million and currency translation losses wkre 7 cents a share.

In the first half, Monsanto earned $221.3 million ($6.08) on sales of $3.15 billion against $211.8 million ($5.80) on sales of $2.53 billion.

The company said it expected sales growth in the second half to fall behind the pace of the first six months.

With a boost provided by its merger with Del Monte Corp., R.J. Reynolds Industries Inc. reported second-quarter net income of $136.9 million ($2.61 a share), up from $111.8 million ($2.28) a year earlier.

Sales totaled $2.25 billion, 31 percent higher than $1.72 billion in the 1978 second quarter.

In the first six months, net income totaled $268.3 million ($5.18) on sales of $4.22 billion against $206.8 million ($4.22) on sales of $3.3 billion. The company had a non-recurring gain equal to 21 cents a share in the 1979 first half.

Del Monte acquired Feb. 2, contributed about 16 cents a share to second-quarter earnings, Reynolds said. The company also reported strong performances by its domestic tobacco and energy businesses although transportation earnings dropped from year-earlier levels.

Second-quarter sales of Minnesota Mining and Manufacturing Co. increased 15.6 percent while net income rose 12.9 percent from a strong year-earlier period.

Worldwide sales in the three months ended June 30 were $1.3 billion compared with $1.1 billion in the same period of 1978. Net income rose to $161.6 million ($1.38 a share) from $143.1 million ($1.23) a year ago when quarterly earnings reflected the combined 9-cent-per-share impact of a onetime $6 million capital gain and favorable currency effects of about $4.6 million.

First-half net income came to $313.7 million ($2.68; an increase of 19.6 percent from $262.4 million ($2.26) in the same period last year. Sales for the first half advanced 17.9 percent to $2.6 billion from $2.2 billion.

Lewis Lehr, vice chairman and chief executive officer said U.S. customers appear to have purchased additional 3M products in March to protect themselves against work stoppage in the trucking industry, shifting some sales from the second quarter to the first.

American Can Co. reported earnings of $1.79 a share for the second quarter against $1.52 a year ago and predicted record profits for the year. First half profit was $2.92 a share, up from $2.50 last year.

Net income for the quarter was $35.4 million on sales of $1.139 billion compared with $30.1 million on sales of $980.4 million. First-half net was $58.7 million on sales of $2.176 billion against $49.6 million on sales of $1.855 billion.

Chairman William F. May said the company's oil, chemical and consumer product operations prospered as well as its metal, plastic and paper container businesses.

Gannett Co., owner of 80 newspapers and 19 broadcast stations in the United States and Canada, reported yesterday that its net profit rose 19 percent in the second quarter of this year compared with the same period last year.